TSA 2010: Dimple Derby

The hot new trend for CO2 racer design in 2010? Dimples. Not the dimples adorning the cheeks of smiling spectators, mind you – we’re talking about race car dimples! Imagine dozens of tiny, golf ball-like depressions meticulously sculpted on the surface of a car body. No fewer than six bedimpled entries found their way to Baltimore for the 2010 TSA CO2 racing events.

While the dimples create an interesting aesthetic, most competitors employed them to gain an aerodynamic edge over the competition. As explained by Gus Cata of Colonial Forge High School in Stafford, Virginia, “The dimples create a layer of turbulent air around the car.” As a car rockets down the track, it leaves an invisible wake behind it. The wake is formed by air molecules – separated by the moving car body – coming back together behind the car. Within the wake, a low-pressure area – a vacuum, if you will – develops that can actually hinder the forward motion of the car. Gus’s research led his team to believe that the dimples on the car’s surface would minimize the speed-inhibiting wake. The team put their theory to the test – their car was the lone dimpled entry in the F1 class.

The inspiration? Try Lance Armstrong’s cycling suit. For the 2004 Tour de France, Nike designers employed wind tunnel testing and created Lance a suit designed to minimize the slipstream, or low-pressure area just behind the rider's body. The suit featured small depressions – dimples – on the arms and shoulders.

The Mythbusters crew experimented with dimples on this Ford Taurus.

MythBusters, the popular Discovery Channel TV series, may have had something to do with the sudden popularity of dimple designs. In a 2009 episode, hosts Adam and Jamie tested the idea that applying golf ball-like indentions to an automobile will improve its fuel efficiency. The results of the experiment surprised both hosts – the dimpled car had an 11% fuel efficiency advantage over its non-dimpled counterparts. If dimples provide enough aerodynamic benefit to improve a passenger car’s fuel efficiency, then why wouldn’t this translate into greater speed on the CO2 racetrack?

TSA car builders used a variety of techniques to make the dimples. A.J. Denton of Caverna High School in Horse Cave, Kentucky, used a drill press. His ultracool Titleist car pays homage to the golf ball and won first place at the Kentucky state competition prior to the national event. A.J. took special care to make each depression a uniform depth. Kiersten Marshall used a Dremel tool. Her car – dubbed Envy – sported a superb paint job despite the fact that the dimpled surface was more challenging to finish. Envy was also the fastest of the dimple cars – finishing 17th in the middle school time trials. That’s only one place shy of becoming a finalist in the middle school event.

So, do dimples equal speed, or are they just a passing fancy? Kiersten and the Pitsco race crew decided to put this to the test. Kiersten volunteered two cars for the unofficial challenge: Envy and a second car having no dimples but otherwise very similar in design. (The second car was not entered in the official event.) The two cars were staged on the track for a head-to-head battle. The Christmas lights lit up in sequence, and the launch pods triggered with the familiar “PSSSST!!!” Both of Kiersten’s cars zoomed down the track. The victor? The non-dimpled racer took the win, knifing its beak across the finish line just ahead of its dimpled sibling.

While the challenge was fun and interesting, it was not conclusive. Very subtle differences in the two cars’ shapes, rolling resistance, or weight could have accounted for the race outcome.

The jury may still be out on dimpled cars, but one thing is clear – competitors in CO2 racing events will leave no stone unturned to gain a competitive advantage. They absorb knowledge and insight from a variety of sources and then apply it to their car designs. This type of critical thinking is what hands-on competitions are all about.